(CNN) -- Tony Snow, former White House press secretary under President Bush, has joined CNN as a political contributor. Snow discussed the 2008 presidential race Monday on "Larry King Live" following an appearance by Sen. Hillary Clinton.

TONY SNOW: On substance, there's not a huge difference between her and Barack Obama on key issues. It comes down to personality. For many Obama voters, it is "we like him." Hillary Clinton's trying to make the argument that he is really not quite ready for prime time. ... There are things in his background that he has to rectify. I think she fairly artfully laid out some of the themes that are going to go on.

But she's also right, this is not a campaign that ends tomorrow, although a lot of people want it done tomorrow. This is going to go through June.

KING: What about the suggestion of Republicans in [Clinton's] Cabinet?

SNOW: Barack Obama's figured out a couple of things. No. 1, people want optimism. No. 2, they want a sense of national unity. So she's laid out that she might have Republicans in. But there's nothing in the record the last few years to indicate that Sen. Clinton ... is going to reach out to Republicans or agree with them on much of anything.

KING: Who's going to win [the Pennsylvania primary]?

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SNOW: I guess Hillary's going to win. But it's interesting, her biggest opponent right now is not Barack Obama. It's conventional wisdom, because everybody's trying to set a margin. The fact is, you win, you win. And the argument that she's been making -- I think it's pretty compelling -- you win the big traditionally Democratic states. If Barack Obama's getting ahead in Republican states, do you have a candidate who's going to be able to propel you to victory?

KING: How do you see November?

SNOW: I think [Sen. John] McCain's going to win, actually, because I think security and the economy both break his way.

But on the Democratic side ... you have got this charisma and emotion on the part of Obama. Can people stay in love with him from now until November? If so, it makes him a stronger candidate. If, on the other hand, the more you learn about him, the more you fall out of love, that's a campaign that could collapse.

Meanwhile, with Hillary Clinton, you have somebody who is battle tested. You have a political machine. You have a lot of experience. And you're going to have the ability to do whatever it takes to try to pull the party together. If you need that kind of machine operation, I think she does better.E-mail to a friend